Demand uncertainty and lot sizing in manufacturing systems: the effects of forecasting errors and mis-specification

This paper proposes a methodology for examining the effect of demand uncertainty and forecast error on lot sizing methods, unit costs and customer service levels in MRP type manufacturing systems. A number of cost structures were considered which depend on the expected time between orders. A simple two-level MRP system where the product is manufactured for stock was then simulated. Stochastic demand for the final product was generated by two commonly occurring processes and with different variances. Various lot sizing rules were then used to determine the amount of product made and the amount of materials bought in. The results confirm earlier research that the behaviour of lot sizing rules is quite different when there is uncertainty in demand compared to the situation of perfect foresight of demand. The best lot sizing rules for the deterministic situation are the worst whenever there is uncertainty in demand. In addition the choice of lot sizing rule between ‘good’ rules such as the EOQ turns out to be relatively less important in reducing unit cost compared to improving forecasting accuracy whatever the cost structure. The effect of demand uncertainty on unit cost for a given service level increases exponentially as the uncertainty in the demand data increases. The paper also shows how the value of improved forecasting can be analysed by examining the effects of different sizes of forecast error in addition to demand uncertainty. In those manufacturing problems with high forecast error variance, improved forecast accuracy should lead to substantial percentage improvements in unit costs

Chemistry to biology knowledge transfer does it work? Mapping of TLO’s by multi-evaluation techniques

Engaging and collaborative activities along with peer assessment allows students to deepen their discipline knowledge, practice team work and gain experience in judging the work of their peers. Thus these activities provide a rich context in which their learning is multi-faceted and is promoted in both discipline and generic domains, supporting the science threshold learning outcomes1. This learning was commenced in first year and then built on in a second year subject. Workshops that were based on active learning principles had previously been developed and used in large first year chemistry subjects2 . That innovation was implemented in another science discipline, with chemistry and biology teaching staff working collaboratively to introduce workshop sessions into BIOL213, a second year biochemistry subject. BIOL213 is largely a ‘service subject’ and has a failure rate of concern. The main aims of the teaching innovation were - to support knowledge transfer from one set of science discipline staff to another, to demonstrate proof of concept, to foster sharing of learning design across the faculty of science especially to research focused staff, to promote deeper student learning through active learning and consequently improve student performance. The evaluation of this innovation aimed to determine whether these teaching activities and assessment tasks had been effective in students achieving these learning outcomes, at threshold level or above, and to help map chemistry and biology disciplinary areas against the science TLOs. The project team were supported by advice, peer review, and leadership training from SaMnet action-learning team. 1.Jones, S and Yates B. 2011 SCIENCE Learning and Teaching Academic Standards Statement, September 2011. ISBN: 978-1-921856-29-7, http://www.olt.gov.au/system/files/resources/altc_standards_SCIENCE_240811_v3.pdf 2 O’BrienG and Bedford, S. (2012) Small group work in large chemistry classes: Workshops in First Year Chemistry. HEAcademy STEM Annual Conference 2012. http://www.heacademy.ac.uk/assets/documents/stem-conference/Physical_20Sciences/Glennys_OBrien.pd

Forecasting Intermittent Demand by Hyperbolic-Exponential Smoothing

Croston's method is generally viewed as superior to exponential smoothing when demand is intermittent, but it has the drawbacks of bias and an inability to deal with obsolescence, in which an item's demand ceases altogether. Several variants have been reported, some of which are unbiased on certain types of demand, but only one recent variant addresses the problem of obsolescence. We describe a new hybrid of Croston's method and Bayesian inference called Hyperbolic-Exponential Smoothing, which is unbiased on non-intermittent and stochastic intermittent demand, decays hyperbolically when obsolescence occurs and performs well in experiments.Comment: Earlier versions of this work were presented at the 25th European Conference on Operations Research, 2012; and at the 54th Annual Conference of the UK Operational Research Society, 2012. A journal version is in preparatio

The Social context of motorcycle riding and the key determinants influencing rider behavior: A qualitative investigation

Objective: Given the increasing popularity of motorcycle riding and heightened risk of injury or death associated with being a rider, this study explored rider behaviour as a determinant of rider safety and, in particular, key beliefs and motivations which influence such behaviour. To enhance the effectiveness of future education and training interventions, it is important to understand riders’ own views about what influences how they ride. Specifically, this study sought to identify key determinants of riders’ behaviour in relation to the social context of riding including social and identity-related influences relating to the group (group norms and group identity) as well as the self (moral/personal norm and self-identity). ----- ----- Method: Qualitative research was undertaken via group discussions with motorcycle riders (n = 41). Results: The findings revealed that those in the group with which one rides represent an important source of social influence. Also, the motorcyclist (group) identity was associated with a range of beliefs, expectations, and behaviours considered to be normative. Exploration of the construct of personal norm revealed that riders were most cognizant of the “wrong things to do” when riding; among those issues raised was the importance of protective clothing (albeit for the protection of others and, in particular, pillion passengers). Finally, self-identity as a motorcyclist appeared to be important to a rider’s self-concept and was likely to influence their on-road behaviour. ----- ----- Conclusion: Overall, the insight provided by the current study may facilitate the development of interventions including rider training as well as public education and mass media messages. The findings suggest that these interventions should incorporate factors associated with the social nature of riding in order to best align it with some of the key beliefs and motivations underpinning riders’ on-road behaviours

Human cryptochrome exhibits light-dependent magnetosensitivity

Humans are not believed to have a magnetic sense, even though many animals use the Earth's magnetic field for orientation and navigation. One model of magnetosensing in animals proposes that geomagnetic fields are perceived by light-sensitive chemical reactions involving the flavoprotein cryptochrome (CRY). Here we show using a transgenic approach that human CRY2, which is heavily expressed in the retina, can function as a magnetosensor in the magnetoreception system of Drosophila and that it does so in a light-dependent manner. The results show that human CRY2 has the molecular capability to function as a light-sensitive magnetosensor and reopen an area of sensory biology that is ready for further exploration in humans